The present invention relates to a flat eccentric rotor equipped with a fan and a flat vibration motor equipped with a fan comprising the rotor, and more particularly to cooling and noiseless alarm means.
Portable devices such as cellular phones have become more multifunctional, and the conduction time in intermittent operation for demonstrating a vibration function, e.g., of silent alarm means of such multifunctional portable communication devices has increased. Flat vibration motors of a brushless type that have a long service life and flat vibration motors of a coreless type that have high efficiency have come to use following the transition to thin devices.
Cored motors in which armature coils are wound about a plurality of protruding poles that are arranged equidistantly and a drive circuit member is disposed laterally of a stator are known as brushless vibration motors comprising a drive circuit member. An example of such a device is found in Japanese Patent Application Laid-open No. 2000-245103.
However, such motors are large in size in the lateral direction, the efficiency of wiring to a printed circuit board is poor when the motor is set up, and because the motor is of a cored type, it inevitably has a large thickness and is not suitable for practical use.
Furthermore, cored and coreless motors in which an empty space is provided by removing some of a plurality of armature coils and a drive circuit member is disposed in this empty space are also known. Such a motor is disclosed in Japanese Patent Application Laid-open No. 2002-142427.
Brushless motors are typically of a single phase type using one Hall sensor to save cost, but a detent torque generating member that stops the magnet of the motor in a specific position is necessary to self-start the single-phase brushless motor.
Functionality of cellular phones etc. has recently greatly improved, and a problem of heat generation by active electronic components contained therein has assumed great importance. In particular, cabinet cases with zones where a large amount of heat is locally generated, e.g., by a CPU, become hot and inconvenient for people during operation.
Some suggestions to accommodate fixed elements for heat absorption and dissipation, such as ceramic sheets, carbon-graphite sheets, and heat pipes, in order to dissipate locally generated heat have been employed, but the problem can hardly be resolved only by heat absorption by such fixed elements, and the installation of a fan motor serving to circulate air forcibly can be considered.
Units with a size reduced to a square with a side of 20 mm and having a heat sink disposed in the radial direction have recently become known. Such a motor is disclosed in Japanese Patent Application Laid-open No. 9-107653.
However, they are still too large to be accommodated in portable devices, for example, cellular phones.
On the other hand, a flat coreless vibration motor is known which comprises a plurality of hollow armature coils and an eccentric weight made from tungsten and disposed in a space where no coils are located and in which an eccentric rotor integrated with a resin is driven with an axial-gap magnet. Such a motor is disclosed in Japanese Patent Application Laid-open No. 3514750.
A vibration motor comprising a fan in which an eccentric weight is mounted on an output shaft of a cylindrical motor was disclosed and used, this motor additionally having an impeller formed on an outer periphery of the eccentric weight. Such a motor is disclosed in Japanese Patent Application Laid-open No. 2004-72420.
However, with such configuration, because an impeller is additionally provided on the eccentric weight, the risk associated with rotation cannot be ignored. Due to the impeller, a revolution outer periphery has to be considered more thoroughly than the motor body and design restrictions are placed on the configuration.
Furthermore, a large motor of an inner rotor type has been suggested as a brushless vibration motor equipped with a fan and comprising a cored armature, this motor having a large length in the axial direction and having a through hole opened eccentrically without changing the diameter of the cored rotor, wherein cooling is carried out by a process in which the air flows into the hole due to the rotation of the rotor and this air is spread in the radial direction by a centrifugal fan that is disposed axially. Such a motor is disclosed in Japanese Patent Application Laid-open No. 2002-165406. However, such motor is too large to be accommodated in a portable device, for example a cellular phone, and does not match a trend toward thickness reduction.